1 April 2012

Is evolution in danger of extinction?

Everyone is familiar with the concept of extinction. Sometimes species are lost forever, whether it is due to natural and unavoidable catastrophes like a large asteroid hitting our planet, which many scientists believe wiped out the dinosaurs, or due the activities of humans. The extinction of a species is sad, but the brutal fact is that it is not all bad and the death of one species allows the evolution of another to occur and fill the now empty niche. A good example is that the mass extinction of the dinosaurs allowed the previously oppressed group of mammals to evolve and become one of the most dominant forms of life on the planet, which has worked out pretty well for us... These events are called extinction spasms and follow all mass extinction events, with the 'bounce-back' time of species taking millions of years. For example, it took 20 million years after the Cretaceous Tertiary Extinction Event for the surviving marine invertebrates to establish as many new families of organisms as they'd lost.

The Barringer Crater in Arizona is 1 mile wide and 570 feet deep. It is believed to be the crash site of the city-sized KT asteroid that hit the Earth 65 million years ago with the force of million nuclear bombs, wiping out half the life-forms on the planet, including the dinosaurs.

Therefore, life has always recovered after mass extinction events and many new species have appeared after them. This is mainly because the past five mass extinction events have left many of the key environments for evolution intact, such as rainforests and underwater environments. Such environments are sometimes called 'evolutionary powerhouses' and are critical for the development of new species, having produced substantially more new species of organism than any other environment, including almost every major group of vertebrate.

The planet is currently undergoing its sixth and largest mass extinction event, which is due to the destructive activities of humans. The most damaging of our activities are mainly mass hunting and deforestation, which have resulted in many species already falling extinct. The problem with this mass extinction however, which sets it apart from the others, is that we are destroying the powerhouse environments and are killing every other category of animal at the same time, rather than just certain ones. This is resulting in a rapid loss of the planet's overall genetic diversity - diversity that is essential for life to recover after we wake up, stop destroying the planet and take steps to halt the extinction event.

An aerial view of the border between Haiti (left) and the Dominican Republic (right). The heavy logging in Haiti for the charcoal and firewood industries has resulted in mass deforestation and as a result, only 3% of Haiti's forests now remain.

As according to Charles Darwin, evolution works when a gene randomly mutates and that this mutation gives the individual an advantage over others of its species, helping it to survive for longer. Thus, the individual can breed more because it is around for a greater length of time and gradually, the mutated allele (which is naturally selected for), increases in frequency throughout the population of the species. Once a species has gone however, its genes are lost and cannot change or be passed on so their potential for evolving into a new species is also gone. New species usually evolve when separate populations of a particular species live in different environmental conditions and cannot breed with each other. Therefore, the different populations will be under different selection pressures for new genes and will undergo speciation, slowly becoming different subspecies and eventually, different species altogether.

Thus, the recovery of life after a mass extinction event depends upon the species that survive it and the genes that remain - genes cannot just appear from nowhere! Therefore the rapid loss of forested habitats, which have survived remarkably well in past mass extinctions, is greatly reducing the planet's genetic 'resource base' and is pushing even more species extinct. Worryingly, it is looking more and more likely that the process of evolution will become severely limited in its capacity to create new species of life and ultimately, may fail and become extinct itself. If this should happen life on Earth will die (eventually humans will die out as well as we'll have no food) and will not be replaced, leaving the planet as just another barren and lifeless rock drifting through space...

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